1. Field of the Invention
The present invention relates to a non-volatile semiconductor device which is constructed on a semiconductor substrate using phase change material and is capable of storing desired data.
2. Related Art
In recent years, non-volatile memory has been widely used to store data of portable device and the like. As next-generation non-volatile memory, attention is directed toward phase change memory using structural changes of phase change material. For example, the phase change memory has a structure in which a phase change layer is deposited on a semiconductor substrate using a chalcogenide based phase change material, and current is supplied to a predetermined region of the layer via an electrode. Such a structure causes the predetermined region of the phase change layer to change freely between its high-resistance amorphous state and low-resistance crystalline state, and using changes in resistance of the states, it is possible to rewritably store desired data (for example, see U.S. Pat. Nos. 6,590,807B2 and 6,567,296B1). In this case, it is possible to construct multi-bit phase change memory by integrating unit cells each composed of a single MOS transistor to supply power and a single phase change memory element.
However, in the aforementioned conventional phase change memory, since the current for rewriting data is sufficiently large, the gate width of the MOS transistor is required to be increased. The area of a unit cell in the phase change memory is determined by the gate width of the MOS transistor, and it is inevitable that the area is increased. In this case, the entire chip area increases as the storage capacity increases in the phase change memory, resulting in an obstacle to high integration.